PROJECT SUMMARY/ABSTRACT Cocaine use disorder is a sizeable health challenge in the United States for which there are no approved medications for treatment. Vulnerability to environmental and drug-related cues previously associated with cocaine-taking behavior (?cue reactivity?) is thought to trigger cycles of dependence and relapse that contribute to high recidivism rates in cocaine use disorder. Thus an improved understanding of the mechanisms underlying cue reactivity is necessary to generate new pharmacotherapeutic strategies to prevent relapse in cocaine use disorder. Studies indicate that the agranular insular cortex (AIC) may play a key role in regulating cue reactivity by serving as a point of convergence for the interpretation of interoceptive signals and relay of this information to other nodes within corticostriatal circuitry. The excitatory and inhibitory balance in the AIC microcircuitry, maintained by resident glutamate projection neurons and ?-aminobutyric acid (GABA) interneurons, respectively, is critical to its normal function. Alterations in the excitatory/inhibitory balance in the cortex are hypothesized to drive processes engaged in drug seeking behavior in addiction. Serotonin (5-HT) neurotransmission through its cognate G?q/11 protein-coupled 5-HT2C receptor (5-HT2CR) is important in maintaining cortical excitatory/inhibitory balance and in regulating cue reactivity, and these receptors are expressed in the AIC. We propose that one potential mechanism to suppress cue reactivity is through the harmonization of the functional connectivity in the AIC-corticostriatal circuit, controlled by the 5-HT2CR system within the AIC. Employing pharmacogenetic, biochemical, behavioral, genetic, and pharmacological methodologies, the present study will address this hypothesis through two Specific Aims: 1) interrogate the AIC corticostriatial circuity in cocaine cue reactivity, and 2) elucidate 5-HT2CR control of AIC over cue reactivity. The elucidation of the complex regulation of the 5-HT2CR modulation of the GABA:glutamate neuronal interaction within the AIC as it relates to cue reactivity will lead to a better understanding of individual risk factors for relapse in cocaine use disorder. This information will be utilized to inform therapeutic development for prevention of relapse to ultimately address this barrier in the treatment of cocaine use disorder.